Re: [asa] geocentricity

Quoting Randy Isaac <randyisaac@comcast.net>:
> 1. What was the data cited as evidence for geocentricity prior to the
> Kepler/Copernicus era? Would it qualify as a "data-verified theory" as we
> think of it today?

The "immovable earth" would have been one such piece of data. If the earth
doesn't move or even spin then obviously the stars and everything else have to
move (around us) in order to do what is directly observed in the sky. And one
piece of evidence for this (the immovable earth) was that if the earth did
spin or move, then it would leave its atmosphere behind and all the birds
would be blown away in the wind. (Remember that for all they knew, "space"
was the same as our sky -- full of air.) Since an immovable earth avoided
this problem of insufferable winds, I suppose you could say in a crude way
that it was a "data fitting theory". Of course, the scientific method as we
know it wasn't a widespread method of studying the world back then. So
comparing it with what we might call a "data-verified theory" might be a bit
unfair.

>
> 2. What is today the most direct and simplest data/observation that proves
> heliocentricity? What was the first such argument?

The Foucault pendulum you mention below would be a simple evidence helping to
remove the immovable earth stumbling block. But probably the best evidence
for heliocentricity over geocentricity is its “retro-prediction” (or
explanation rather) that so neatly fits the motions of the planets. It was
Keplers’ laws, though, that were needed to really make the fit work nicely.
Then all the pesky retrograde paths of the planets in their elliptical orbits
fell into place. So even though it (heliocentricism coupled with Kepler's
laws) can’t rank as a prediction, it was an extremely powerful explanation of
the existing data. Geocentricity now would be forced to revive all the
extremely awkward explanations for why the planets so
regularly “misbehave.”
>
> 3. What is today the most direct and simplest data/observation that shows the
> earth rotates on its axis? Was Foucault's demonstration of the
> latitude-dependence of the coriolis force the first such evidence?
> Randy

In addition to the explanations above, which should double for an answer to
#3, you could probably add such simple measurable experiments as centripetal
force which counters gravitational acceleration at the equator. Something
more precise than a bathroom scale may be needed to measure such small
differences – but they would be easily calculable and measurable. No spinning
earth -- no centripetal force.

--Merv (ASA member)

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Received on Wed Jul 4 23:55:00 2007